TTField treatment with optimization of electrode positions on the head based on MRI-based conductivity measurements
When electrodes are used to impose an electric field in target tissue within an anatomic volume (e.g., to apply TTFields to treat a tumor), the position of the electrodes can be optimized by obtaining electrical conductivity measurements in an anatomic volume and generating a 3D map of the conductivity directly from the obtained electrical conductivity or resistivity measurements, without segmenting the anatomic volume into tissue types. A location of the target tissue is identified within the anatomic volume, and the positions for the electrodes are determined based on the 3D map of electrical conductivity and the position of the target tissue.
1. A method of creating a model of a mammal's head, the head including brain tissue, CSF, a skull, and a scalp, the method comprising the steps of:
modeling a region of the head that corresponds to brain tissue using a 3D set of conductivity tensors; and
modeling the CSF, the skull, and the scalp using at least one shell having a constant conductivity.
2. The method of claim 1 , wherein the step of modeling the region of the head that corresponds to brain tissue using a 3D set of conductivity tensors is implemented without identifying boundaries between different types of a healthy brain tissue.
3. The method of claim 1 , wherein the 3D set of conductivity tensors is obtained using MRI.
4. The method of claim 3 , wherein the 3D set of conductivity tensors is derived from a diffusion tensor imaging dataset.
5. The method of claim 1 , wherein the step of modeling the CSF, the skull, and the scalp comprises the steps of:
modeling the CSF as a first shell disposed outside the brain tissue and in contact with the brain tissue, the first shell having a first constant conductivity;
modeling the skull as a second shell disposed outside the CSF and in contact with the CSF, the second shell having a second constant conductivity; and
modeling the scalp as a third shell disposed outside the skull and in contact with the skull, the third shell having a third constant conductivity.
6. The method of claim 1 , wherein the step of modeling the CSF, the skull, and the scalp comprises the step of:
modeling the CSF, the skull, and the scalp, taken together, as a single shell disposed outside the brain tissue and in contact with the brain tissue, the single shell having a constant conductivity.
7. The method of claim 1 , further comprising the steps of:
identifying a location of a target tissue within the brain tissue; and
determining positions for a plurality of electrodes on the mammal's head based on the location of the target tissue identified in the identifying step, the 3D set of conductivity tensors, and the conductivity of the at least one shell.
8. The method of claim 7 , further comprising the steps of:
affixing the electrodes to the mammal's head at the positions determined in the determining step; and
applying electrical signals between the electrodes subsequent to the affixing step, so as to impose an electric field in the target tissue.
9. The method of claim 7 , wherein the step of determining positions for the electrodes comprises modeling a dipole at a location that corresponds to the target tissue and selecting positions at which a potential attributable to the dipole is maximum.
10. The method of claim 7 , wherein the step of determining positions for the electrodes comprises calculating positions for the electrodes that will provide optimal combined treatment specifications in the target tissue.
11. The method of claim 1 , wherein the step of modeling a region using a 3D set of conductivity tensors comprises classifying a tissue type for each volume element based on a fractional anisotropy.
12. The method of claim 1 , wherein the step of modeling a region using a 3D set of conductivity tensors comprises classifying a tissue type for each volume element based on a mean conductivity.
13. The method of claim 1 , wherein the step of modeling a region using a 3D set of conductivity tensors comprises matching geometric means of conductivity tensors' eigenvalues to specific isotropic reference values.
14. The method of claim 1 , wherein a composite model is generated in which the modeled region of the head that corresponds to brain tissue is surrounded by the modeled CSF, skull, and scalp using the at least one shell.